Variable resistance memories have been known as nonvolatile semiconductor memory devices. A variable resistance memory is a memory in which two-terminal variable resistance elements each having a variable resistance layer interposed between two electrodes are used as memory elements. In such a variable resistance memory, information writing and reading are performed by utilizing reversible changes in the variable resistance layer between a high-resistance state and a low-resistance state in accordance with the history of voltage application between the electrodes. Even if the voltage between the two electrodes is cut off, the resistance state of the variable resistance layer is maintained. Therefore, such a variable resistance memory is a type of nonvolatile memory.
Variable resistance elements are classified into several types on the basis of the types of variable resistance layers and electrodes. For example, there are redox variable resistance elements that utilize movement of oxygen defects in transition metal oxides, ion-conducting variable resistance elements that utilize movement of metal ions or the like in the variable resistance layers, and the like.